to talk about past experiences when we don’t say when something happened (when the action was finished). Example: I’ve travelled to Brazil many times.
with yet, already, ever, and never. Example: I’ve already finished my homework.
with superlatives and the first, second, the last time, etc. Example: Canada is the most beautiful place I’ve visited.
with non action verbs (= verbs not usually used in the continuous form, for example, be, have, know, like, understand, believe, etc) to say that something started in the past and is still true now. Example: I‘ve known my best friend since we were in high school.
when we say or ask how much/many we have done or how often we have done something up to no (so far). Example: I’ve written 5 essays so far.

with action verbs, to say that an action started in the past and is still happening now. Example: I’ve been writing this article for 2 hours.
this use is common with time expression such as How long …?, for, since, all day/morning/afternoon/evening/ week, etc. Example: I’ve been studying all morning.
for repeated actions especially with the time expression all day, recently. Example: She’s been cleaning her house all day.
for continuous actions that have just finished (but that have present results). Example: I’ve been doing my homework.